Question

I’m having problems with my SQL query again…

D.0.02 has been allocated for day 1 period 1 so it should count 0. But it has not been allocated for day 1 period 2. Why is it returning as 0?

SELECT COUNT(DISTINCT rm.Id)
FROM ts_room rm LEFT JOIN ts_roompref rp ON rp.room_id = rm.id
  LEFT JOIN ts_request rq ON rq.id = rp.request_id
  LEFT JOIN ts_allocation a ON a.request_id = rq.id
WHERE room_id = "D.0.02"
  AND (a.status IS NULL OR a.status IN ('Pending', 'Failed', 'Declined'))
  AND (day_id=1 AND period_id=2)

Here is my fiddle: http://sqlfiddle.com/#!2/5e1de/13

If the status is not Pending, Failed, Declined the room is ignored but it could be free for other period or days but not booked – if it is not booked then it is not allocated – this means that the day_id and period_id will not exist but the room will still be free to book.

It would seem that I would need to retype my SQL query. Any advice on how to?

Answer 1

Count() always returns a number even when no rows match.
In your case, no rows match, so count() returns 0.

Edit:

Your select counts the number of bookings. 0 means that it is unbooked.

If you want to return 1 when it is unbooked you need to reverse it:

SELECT 1 - COUNT(DISTINCT rm.Id) 
FROM ts_room rm LEFT JOIN ts_roompref rp ON rp.room_id = rm.id
  LEFT JOIN ts_request rq ON rq.id = rp.request_id
  LEFT JOIN ts_allocation a ON a.request_id = rq.id
WHERE room_id = "D.0.02"
  AND a.status = 'Allocated'
       AND day_id=1 AND period_id=2

Note that if you make a wider search, for instance all periods in a day, you need to change the 1 to the number of periods (9) to return the number of free slots.